The invention relates to a pipetting device for metering liquids.
Pipetting devices are used in laboratories for metering liquids. Air cushion pipettes have at least one integrated displacement unit comprising a cylinder and a piston arranged longitudinally displaceably therein. The hollow space of the cylinder is connected via a connecting channel to a through-hole in a seat for a pipette tip. By displacing the piston in the cylinder an air column may be displaced, in order to draw sample liquid into a pipette tip arranged sealingly on the seat and to eject sample liquid therefrom. In this connection, the displacement unit does not come into contact with the liquid. Only the pipette tip, which generally consists of plastics, is soiled and may be replaced after use,.
The piston is connected to a drive for displacing the piston within the cylinder. It is known to couple to the piston rod a piston actuating rod which may be driven manually or by means of an electromotive linear drive. The piston rod is inserted into a receiver of the piston actuating rod. Additionally, a spiral spring or helical spring is inserted into the receiver which rests against the piston spring in a pretensioned state, in order to avoid play.
The assembly cost for the known pipetting device is high, in particular because the exceptionally small spring is difficult to handle. This is also disadvantageous during use, for example when the user disassembles and reassembles the pipetting device for cleaning or autoclaving or for the replacement of faulty parts.
Proceeding therefrom, the object of the invention is to provide a pipetting device in which the assembly and disassembly of the piston actuating rod and displacement unit is associated with a lower cost.